The present invention relates to an optical engine for fingerprint reader, especially an integrated optical prism with double functions of prism and lens for replacing optical engines of traditional fingerprint readers that consists of a right-angle prism and a lens. The present invention simplifies the assembling of components and increases the stability and reliability of the optical engine.
The optical engines for fingerprint readers available on the market are based on various materials such as optical fibers, capacities, or traditional types. However, except traditional types, others need higher cost. Thus traditional-type optical engine is still the main stream of market. Refer to FIG. 1, a traditional optical engine 10 is composed by a right-angle prism 11 and a lens 12. The position for finger F 13 is on the inclined optical surface of the right-angle prism 11 while a LED (light emitting diode) light source 14 is disposed on one of the optical surfaces 15 of the right-angle prism 11 (such as horizontal plane shown in figure). By Snell's law, the light emitted from the LED light source 14 is totally reflected on the position for finger F 13 so that the black and white stripes of the fingerprint is projected from another optical surface 16 (the vertical plane shown in figure), finally through a lens 12 forms an image on a sensing device 17. But the optical engine 10 with two-piece structure has following disadvantages:                (1) The structure of assembling of two components has larger volume, thus is difficult to get popular support.        (2) In the two-component structure, the right-angle prism 11 and the lens 12 shall be localized precisely so as to make the light path straight. Not only the number of components causes the problem, but the difficulty of assembling is also increased. Thus the cost is high.        (3) The prism 11 is a right angle prism so that an image of the LED light source 14 also forms on the sensing device 17. This leads to the low S/N ratio that has bad effect on efficiency of the device.        (4) The position for putting finger F 13 is a flat plane so that users need to press in order to get the clear fingerprint image. This causes a bit inconvenience.        